What types of bugs are generally considered release blockers?

Issues that affect the critical path stuff (graphics, installer, network) have a lower barrier because fixing them with updates is much more disrupting.

Why aren't sound or audio bugs considered blocker bugs?

Sound issues have a very high barrier to being release blockers, because they can be fixed well with an update.

I have identified a bug that I believe is a blocker. Is it okay if I just add it?

If you have reviewed the blocker criteria for the release and believe your bug meets the criteria, definitely add it. When in doubt add it to the blocker list. Better to add it and have it removed versus never getting a thorough review.

What is the Target Release tracker bug for?

The Target tracker is a nice to have fixed list of bugs for a release. It is a convenient way to separate them from all the other open bugs a maintainer may be following.

Is there a list of all the blocker bugs for a release?

What about hardware and local configuration dependent issues?

Many bugs are not universal: they only affect certain hardware or software components, or certain configurations or combinations of hardware and software components. When a bug causes a criterion not to be met in some but not all cases, the teams involved in the release process will make a judgement as to whether the impact of the bug is severe enough to consider the release as a whole not to meet the release criteria. This judgement will be based on multiple factors:

The amount of users, overall, the issue is estimated likely to affect

The ease with which the issue can be worked around by documentable configuration changes

The difficulty involved in fixing the issue: whether there is a significant chance that attempting to fix the issue could cause more serious problems